Tree-ring Data from Treelines near the John River, central Brooks Range, Alaska, 1832-2021

The position of the Arctic treeline is an important regulator of land surface energy budgets, ecosystem-atmosphere carbon cycling, wildlife habitat and availability of subsistence resources to local communities. The prevailing hypothesis states that treeline position is determined by air temperature during the growing season. Because trees are taller than tundra vegetation and their canopy extends above the warmer boundary layer, their tissues are colder than tundra vegetation. These colder conditions are hypothesized to limit cell division and growth, such that seedlings are unable to grow into trees. However, our early work revealed that air temperature is warmer than previously thought near the Arctic treeline in Alaska and the indirect effects of temperature on soil nutrient availability may be important determinants of tree growth. We hypothesized that cold soils at treeline, particularly during winter, limit microbial activity and nutrient availability to the point where trees are barely able to survive and grow. This dataset contains tree-ring measurements made on increment cores collected in late August of 2021 at three treelines that varied in soil moisture and tundra vegetation near the John River in the central Brooks Range (Gunsight = dry heath tundra, Eagle Creek = mesic shrub tundra. Sheep Pond = wet sedge tundra). Our objective was to relate the tree-ring data to the weather record for Bettles, Alaska and test the hypothesis that winters with greater precipitation and/or deeper snow were associated with greater tree growth.